Carbon nanotubes have been employed in connection with selectively permeable membranes for some time. Despite this work, various problems remain to be solved. For example, conventional fabrication methods for such membranes tend to suffer from problems such as: limited choice of membrane materials, difficulty achieving large and uniform membranes, and/or disappointing membrane performance (e.g. poor results relative to small-scale proof of concept work). Accordingly, it would be an advance in the art to alleviate these issues.